There are numerous television and video digital signal sampling rate standards. For example, a sample rate of 13.5 MHz is compatible with the 4:2:2 Component Digital Standard (CCIR 601). Sampling at this rate produces 720 active video samples per linearized line on a standard television tube as is also referred to as standard definition television (SDTV). SDTV displays 525 lines per image frame in interlaced mode. High Definition Television (HDTV) has not yet been standardized, but may sample in the range 72 MHz to 81 MHz. The International Radio Consultative Committee, CCIR, has proposed a sample rate of 1920 samples (pixels) per line for HDTV. One HDTV standard can display 1125 lines of resolution per image frame, as compared to the 525 lines of standard definition television. Other television standard exist, such as the D2-MAC, PAL and SECAM standards, in Europe and the Wide Screen Television (WST) standard.
With the many standards in existence, it is desirable to be able to convert from one standard to another, such as for the display of a television/video signal recorded in one standard format on a television set designed for display of a different standard format.
In some instances, this is referred to as video resizing. For example, video resizing allows a full length motion picture film (start on 35 mm, 24 frame film) having a 16 by 9 aspect ratio to be displayed on an NTSC television set without having to "letter box" the output display. In the digital domain, video resizing requires that the input signal be digitally resampled.
Digital resampling produces a different representation of the digital input signal by calculating points of the signal that did not necessarily exist in the original signal. New samples are generated in locations which did not previously have samples through an interpolation technique. A flexible interpolation filtering architecture is capable of resizing a video/television line to an arbitrary size. An example of video resizing is described in U.S. Pat. No. 08/317,474 issued Nov. 4, 1994, entitled FILTER SELECTION CIRCUIT FOR DIGITAL RESAMPLING SYSTEM, which is incorporated by reference herein.
Another example of video resizing takes place in picture-in-picture television displays. U.S. Pat. No. 4,652,908 issued Mar. 24, 1987 entitled FILTERING SYSTEM FOR PROCESSING A REDUCED RESOLUTION VIDEO IMAGE, describes a system for video signal processing to produce a reduced size image for display inside of a larger image television screen. This system involves a reduction of the signal to an already known, smaller picture size.